The invention has application where it is desired to switch select one of a plurality of modulated carrier signals. In the prior art it has been common to switch one of a plurality of signal sources to an output terminal. Typically, a plurality of tank-circuits, such as crystal elements, is connected to a switch and the desired one is coupled to an oscillator. The oscillator output is then fed to a modulator, the tuned circuit of which is switch selected by an element ganged to the oscillator switch. The modulator output is then made up of the modulated component of the oscillator signal. This system requires a very complex switch, which, with its attendant wiring, tends to produce spurious coupling of unwanted signals. Also the switch being remote from the tank circuits means that long signal paths must be used and this introduces stray parasitic reactances than can adversely affect the behavior of the signal circuits.